Twisted light microgears advance optical computing potential

An international research collaboration led by the University of Southampton's School of Electronics and Computer Science (ECS) and the Optoelectronics Research Centre (ORC) has demonstrated tiny vortexes of twisted light that will enable higher capacity data transmission in optical computing.

The innovation, which uses microgears to twist light around an axis much like a corkscrew, makes use of chemical element germanium that is compatible with the silicon used to make computer chips.

Southampton researchers together with partners from the University of Tokyo, Toyohashi University of Technology and Hitachi Ltd, all in Japan, have described the new light-emitting gears in The Optical Society journal Optics Express. With a radius of one micron or less, 250,000 of these gears could be packed into just one square millimetre of a computer chip.

Lead author Abdelrahman Al-Attili, of Southampton’s School of Electronics and Computer Science, explains: “Our new microgears hold the potential for a laser that can be integrated on a silicon substrate— the last component needed to create an integrated optical circuit on a computer. These tiny optical-based circuits can be based upon the principle of twisted light, which makes it possible to transmit larger amounts of data.â€?

In conventional computing, light is used to carry information by varying the number of photons emitted or switching between light’s two polarisation states. With twisted light, or orbital angular momentum, each twist can represent a different value or letter, allowing the encoding of more information using less light.

This new research, which was supported by the Engineering and Physical Sciences Research Council (EPSRC), avoids the poor light emission efficiency qualities of silicon by expanding upon the material properties of germanium. The solution features microgears that are stretched by an oxide film.

“Previously, the strain that could be applied to germanium was not large enough to efficiently create light without degrading the material,â€? Abdelrahman says. “Our new microgear design helps overcome this challenge.â€?

The researchers used electron beam lithography to fabricate the very fine physical features that form the gears’ teeth. They then illuminated the gears with a standard green laser. After the microgear absorbed the green light it generated its own photons that circulated around the edges, forming twisted light that reflected vertically out of the gear by the periodic teeth.

The researchers optimised their design using computer simulations that model the way light propagates in the gears over a period of less than a nanosecond. By comparing a prototype’s light emission with computer simulation results, they were then able to confirm that the gears generated twisted light.

The researchers are now working to further improve the efficiency of light emission from the germanium microgears. If successful, this technology would make it possible to integrate thousands of lasers onto a silicon chip for transmitting information.

“Silicon fabrication technologies that were developed to make electronic devices can now be applied to make various optical devices,â€? Abdelrahman says. “Our microgears are just one example of how these capabilities can be used to make nano and microscale devices.â€?